Their opponents are calling it desperate opportunism, but the Labour Party insists their black billboards are nothing more than a clever way to show support for the All Blacks.

About 40 billboards around Auckland and Wellington have recently popped up with white lettering on a black background: "When things look black, we're at our best."

Below that in red letters is: "Go the boys."

The billboard has been mocked on right-wing blogsite Kiwiblog as desperate, and Labour's campaign spokesman Grant Robertson was not shy about the link to the national rugby team.

"There's multiple layers of meaning. We want to show some support for the All Blacks."

The message was not meant to convey that Labour was close to toast this election, he said. "We're facing a significant challenge. We recognise that. We think we can win.

"People shouldn't be reading deeply into the tea leaves ... We're showing support for the All Blacks while having a light-hearted poke at ourselves at the same time.

"I think people will get that."

The team that put the billboard together were aware of potentially falling foul of advertising rules around the Rugby World Cup, which explains the absence of the words "All Blacks" in the message.

The billboards were put up within hours of being conceived, but Mr Robertson did not have the exact cost of the billboards.

"People have a wide variety of views on billboards in all parties.

"I'm sure if you asked the Green Party about their billboards, there will be a wide variety of views. I'm sure there will be in the National Party as well."

Meanwhile former rugby and rugby league star Matthew Ridge is still awaiting the Electoral Commission's decision on whether billboards advertising his carwash business have broken the law.

Four billboards across Auckland feature a picture of Ridge and the slogan: "Say no to Labour - We'll hand wash your car for $15".

Chief electoral officer Robert Peden has said it meets the definition of an election advertisement under the Electoral Act, meaning Ridge could face a fine of up to $10,000.

Ridge said yesterday that the billboards were still up.

"But we'll move to rectify any problems, should the Electoral Commission think we've stepped outside the law. From our point of view, it's a bit ridiculous.

"I didn't realise the Electoral Commission had copyright on the word 'labour'."

But he said business was booming.

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Prime Minister John Key's DJ shows are likely to come under close scrutiny after Labour complaints to the Electoral Commission about a radio segment he hosted last week.

Mr Key hosted an hour-long programme on RadioLive on Friday. It included interviews with a number of celebrities including Sir Peter Jackson and Richie McCaw.

During the show, Mr Key told listeners the hour was an "election-free zone", and spent the time discussing issues ranging from his cat to Coronation St.

At the time, a spokeswoman for the PM said the station had stipulated the hour had to be free of politics, after advice from the Electoral Commission that political content could breach election rules.

However, the Labour Party is arguing that his stint still broke the rules and yesterday lodged complaints with the Electoral Commission and the Broadcasting Standards Authority.

Labour Party general secretary Chris Flatt said Mr Key's hour breached the prohibition on paid election programmes, breaking the Election Programmes Code of Broadcasting Practice and being an unauthorised election advertisement.